The US attorney accused of hounding internet activist Aaron Swartz to his death has responded by saying that her office's actions were "appropriate", and that she had only been seeking a six-month sentence in "a low-security setting" rather than the 30 years' jail that his actions might have attracted.

Carmen M Ortiz, the federal prosecutor for Massachusetts, defended her actions, said her office acted reasonably and had recognised that Swartz wasn't trying to gain financially from his actions.

Ortiz has come under sustained pressure since Swartz, 26, was found dead less than a week ago. She has been described as a "bully" after the death of the activist and co-founder of Reddit caused an outpouring of grief online – an online petition at the White House calling for her removal from office attracted more than 25,000 signatures.

The backlash from what has been seen as an insensitive approach to a case, in which nobody lost money and no complaints were raised, could damage any further political ambitions she might hold.

Swartz's parents reacted furiously, accusing prosecutors of being over-zealous, while Zoe Lofgren, a Democrat representing part of Silicon Valley, says she will try to narrow the scope of the law under which Swartz was prosecuted. Though Swartz's lawyers were trying to work out a plea bargain before his death, a key sticking point was apparently that the prosecutor was insisting on a jail term of some kind.

Swartz, 26, was found dead at his home in Brooklyn on January 11, apparently having committed suicide after repeated failure to get the charges brought by Ortiz dropped or reduced. He was accused of using the computer network at the Massachusetts Institute of Technology (MIT) to download about 4m academic articles from the JSTOR database, with the intention of redistributing them for free. JSTOR did not object to his actions, but Swartz was arrested and charged in January 2011 with a number of offences including wire fraud and computer fraud, which in the US attract significant penalties.

Ortiz, the federal prosecutor who led the case against Swartz, said in a statement on Wednesday evening that she extended her "heartfelt sympathy to everyone who knew and loved this young man", and that as a parent and a sister "I can only imagine the pain felt by the family and friends".

But she insisted that her office "took on the difficult task of enforcing a law they had taken an oath to uphold, and did so reasonably". In the statement, she accepts that "there was no evidence against Mr Swartz indicating that he committed his acts for personal financial gain, and they recognised that his conduct – while a violation of the law – did not warrant the severe punishments authorised by Congress and called for by the Sentencing Guidelines in appropriate cases. That is why in the discussions with his counsel about a resolution of the case this office sought an appropriate sentence that matched the alleged conduct – a sentence that we would recommend to the judge of six months in a low security setting."

Swartz's lawyer could have called for probation, she noted, but warned too that "ultimately, any sentence imposed would have been up to the judge".

That is at odds with the position frequently put forward by Ortiz herself, who said after Swartz was charged in July 2011 that "stealing is stealing, whether you use a computer command or a crowbar, and whether you take documents, data or dollars."

Swartz apparently sought to redistribute the papers online because he objected to the principle by which JSTOR paid publishers rather than the papers' authors. JSTOR said publicly that it would not seek to bring any civil charges against him, and shortly before his death announced that it would make about 4.5m of its articles available online for free.

Ortiz's statement reads: "As a parent and a sister, I can only imagine the pain felt by the family and friends of Aaron Swartz, and I want to extend my heartfelt sympathy to everyone who knew and loved this young man. I know that there is little I can say to abate the anger felt by those who believe that this office's prosecution of Mr Swartz was unwarranted and somehow led to the tragic result of him taking his own life.

"I must, however, make clear that this office's conduct was appropriate in bringing and handling this case. The career prosecutors handling this matter took on the difficult task of enforcing a law they had taken an oath to uphold, and did so reasonably.

"The prosecutors recognised that there was no evidence against Mr Swartz indicating that he committed his acts for personal financial gain, and they recognised that his conduct, while a violation of the law, did not warrant the severe punishments authorised by Congress and called for by the Sentencing Guidelines in appropriate cases. That is why in the discussions with his counsel about a resolution of the case this office sought an appropriate sentence that matched the alleged conduct — a sentence that we would recommend to the judge of six months in a low security setting. While at the same time, his defense counsel would have been free to recommend a sentence of probation. Ultimately, any sentence imposed would have been up to the judge. At no time did this office ever seek – or ever tell Mr Swartz's attorneys that it intended to seek – maximum penalties under the law.

"As federal prosecutors, our mission includes protecting the use of computers and the internet by enforcing the law as fairly and responsibly as possible. We strive to do our best to fulfill this mission every day."